In 1970, Zolle et al. reported the preparation of metabolizable radioactive human serum albumin microspheres. Int. J. Appl. Radiat., 21, 155-167 (1970). The microspheres were prepared by dispersing droplets of a 25% solution of albumin in heated cottonseed oil with continuous stirring. Solidified microspheres were obtained after heating for 75 minutes at temperatures from 118.degree. to 165.degree. C. The microspheres were separated from the oil by centrifugation, washed free of oil with diethyl ether and dried in air. A similar procedure is described in Zolle U.S. Pat. No. 3,937,668 for incorporating precipitated drugs and other substances in albumin microspheres. According to the Zolle patent, it is necessary to heat the oil in which the microspheres are formed to a temperature above 100.degree. C. to evaporate water and to form the spheric albumin particles having the precipitate encapsulated therein. Scheffel et al prepared albumin microspheres for study of the reticuloendothelial system using a modification of the Zolle procedure. Aqueous albumin was homogenized at room temperature with a small quantity of the oil, and the resulting emulsion was dispersed in a body of oil heated to 175.degree.-185.degree. C. with continuous stirring. On cooling, diethyl ether was added, the microcapsules recovered by centrifugation, washed with diethyl ether, and dried. Scheffel et al. J. Nucl. Med., 13, 498-503 (1972). In 1974, Kramer proposed the use of a similar procedure for preparing albumin microspheres as vehicles for achieving specificity in drug delivery. Mercaptopurine was dissolved in the aqueous albumin prior to conversion to microspheres, and this water-soluble drug was shown to be entrapped in the microspheres. Kramer proposed that sonication could be used to produce smaller and more uniform size particles. Kramer, J. Pharm. Sci., 63, 1646-1647 (1974).